Flux composition for brazing of aluminum material and method for brazing of aluminum material

ABSTRACT

A flux composition for brazing of an aluminum material which can feed a proper amount of flux to an area to be joined at the time of brazing and at the same time can improve working environment, and a method for brazing of an aluminum material. The method comprises: coating an aluminum material to be joined with a flux composition comprising 0.5 to 25 parts by weight of a polymeric compound having a number average molecular weight of 50000 to 5000000 and comprising repeating alkylene oxide units, 5 to 30 parts by weight of a fluoride flux, and water added in such an amount as will provide a total amount of the composition of 100 parts by weight; heating the coated area to remove water; heating the coated area to decompose and remove the polymeric compound; and then conducting heating for brazing.

TECHNICAL FIELD

This invention relates to a flux composition for brazing of aluminummaterials such as in the production of heat exchangers, to a fluxcomposition which is used when brazing parts comprising aluminum or analuminum alloy, to a method of brazing aluminum materials, and inparticular to a method of joining plural parts together by brazing in asingle brazing step.

In this specification, the term "aluminum" is used to mean variousaluminum alloys in addition to pure aluminum.

BACKGROUND ART

Generally, when many hundreds of points have to be joined by brazing asin the case of a heat exchanger, brazing sheets are used for componentpieces such as plates or fins, the assembly being heated in a furnaceafter fitting all parts together and the brazing of plural points beingaccomplished in one heating step.

An example of the use of brazing sheets to assemble aluminum materialsis in the construction of a heat exchanger body, where it was common toemploy preplaced brazing using a preplaced brazing piece such as a pipeor the like. Alternatively, instead of a pipe, a powdered brazing pastewas used as an auxiliary material in the brazing of the heat exchangerbody. In both cases, the aluminum material to be brazed was analuminum-silicon alloy.

In one method of brazing aluminum parts, the aluminum oxide film on thesurfaces of the parts to be joined was removed by a flux. In recentyears, instead of the chlorine type flux material which was previouslyused, a non-corrosive, non-water-soluble aluminum fluoride type flux hasbeen developed. This fluoride type flux is used as a flux for the abovefurnace brazing step. As it is almost non-corrosive, non-water-solubleand non-hygroscopic when compared with the previous chlorine type flux,the fluoride type flux was dispersed in a liquid together with analuminum alloy brazing powder immediately prior to use. This fluxsuspension was then coated onto the parts to be joined by spraying ordipping, and after drying the parts, they were assembled.

According to the prior art, the medium used to disperse this flux wasgenerally water, however as the viscosity of water is extremely low, theadhesion of the flux to the parts to be joined was poor. If adhesion ispoor, the flux easily falls off after coating when the coated surfacesare subject to friction and vibration. This adversely affects theworking environment due to scatter of flux and decline of brazingproperties, and leads to the build-up of foreign matter in the interiorcircuitry of the heat exchanger. Also, as a large amount of flux dripsoff during the coating process, excess flux had to be applied to coverthe loss. This improves brazing properties, but leads to increase offlux residues on the joining surfaces after brazing by heating and againresults in poorer film adhesion during the coating process. If theselarge amounts of residues retain moisture, anti-corrosion properties areimpaired and an unusual odor is produced. Moreover, residues in theinternal circuitry of the heat exchanger increased resistance to theflow of air or coolant and caused heat exchanging performance to fall.

Various flux compositions were therefore proposed to increase theviscosity of the flux suspension and improve its adhesion. In one suchtechnique, the dispersant is an organic solvent, and a resin (e.g.carboxymethylcellulose, rosin, vinyl acetate) is added to increase theviscosity of the vehicle ("vehicle" being a general term for thedispersant of the flux or aluminum alloy powder, i.e. the resin andorganic solvent). For example, JP 07-185796A suggests polyvinyl alcoholas an example of such a resin.

However, there was a problem with this flux composition in that when thetemperature was increased up to the brazing temperature (approx. 600°C.), the external appearance of the product was marred and defects injoins were caused by pyrolysis gases, voids in fillets due tocarbonization and black surface residues. Also pyrolysis products alsoadhered to the aluminum brazing furnace.

Another technique is disclosed for example in JP 08-187594A, wherein aviscous vehicle, comprising a polyalkylene oxide resin dissolved in anorganic solvent, is used as a dispersant. Suitable viscosity is obtainedby dissolving the aforesaid polyalkylene oxide in the solvent, pyrolysisproperties are satisfactory, and carbonization residues are not producedafter brazing. This flux paste is applied to the parts to be joined, andafter heating to vaporize or decompose the components of the vehicle,brazing is performed by the usual method.

However the organic solvent had an unusual odor, and the foul odorproduced on heating gave workers an unpleasant feeling. Some organicsolvents used in the flux paste such as 1,4-dioxane had a highflammability, were toxic to man, and affected workers' hygiene as awhole.

Moreover solvent remained in joins as undecomposed residue, causingdeterioration of brazing properties.

When a viscous vehicle was used as dispersant, adhesion of flux wasimproved compared to the case when water was used, but some flux felloff from joins due to friction or vibration during work performed aftercoating and drying up to the brazing step. Hence, the problems due topeeling flux were still not completely resolved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of a heat exchanger used as a test bodyfor a brazing test according to one embodiment.

FIG. 2 is a perspective view showing part of the heat exchanger of FIG.1.

DISCLOSURE OF THE INVENTION

This invention, which was conceived in view of the above problems, aimsto provide a flux composition and method employing this composition forthe brazing of aluminum materials wherein a flux amount supplied for thebrazing of joins is exactly the right amount, and wherein the workingenvironment is improved.

In order to achieve the aforementioned objectives, the flux compositionfor brazing aluminum materials according to this invention comprises0.5-25 weight parts of a polymer compound having alkylene oxiderepeating units of number average molecular weight 500,000-5,000,000 and5-30 weight parts of a fluoride type flux, the remainder being water tomake the composition up to 100 weight parts.

Water is used as a dispersant for the flux, and as the resin useddecomposes and volatilizes at 140° C.-200° C., the resin component canbe completely removed by performing a simple preheating before thebrazing step, only the flux useful for brazing being supplied to thealuminum materials. There is therefore no risk that the furnace will bepolluted by or that brazing defects will be caused by decompositionresidues of resin components.

The flux composition for brazing of aluminum materials according to thisinvention may also comprise 0.03-5 weight parts of a non-ionicsurfactant.

The non-ionic surfactant has a high affinity with the flux, so the fluxcan be stably dispersed in the composition. The stability of thecomposition over time is therefore improved.

To achieve the aforesaid objects, the method of brazing aluminummaterials according to this invention is characterized in that the fluxcomposition of the invention is coated onto aluminum materials to bejoined, the coated surfaces are heated to remove water, the coatedsurfaces are heated to decompose the polymer compound, and heating isthen performed to accomplish the brazing.

There is no particular limitation on the type of aluminum materialswhich can be brazed by the method of this invention provided that thefluoride type flux of the invention can be applied. Moreover, there isno limitation on the brazing materials used provided that they allow useof the fluoride type flux of the invention.

In the flux composition according to this invention, water is used as adispersant, a water-soluble polymer is used as a binder to conferviscosity, and adhesion of the flux to joins is thereby improved.

Flux composition

Polymer compound

The polymer compound is a substance having repeating units of analkylene oxide such as ethylene oxide or propylene oxide. It may be ahomopolymer of alkylene oxide, or a copolymer with a different type ofalkylene oxide or other compound. Either straight-chain or branchedpolymer compounds can be used. Preferred examples of the polymercompound are polyalkylene oxides obtained by addition polymerization ofa low alkylene oxide such as ethylene oxide with an organic compoundhaving two or more active hydroxyl groups, or a polymer compoundobtained by reaction of such a compound with a polybasic carboxylicacid, its anhydride or low alkyl ester, or a diisocyanate. The terminalgroups of the molecule may comprise alkoxy, carboxyl or ester inaddition to hydroxyl, and there may be ester bonds or urethane bonds inthe molecule in addition to ether bonds.

The number average molecular weight of this polymer compound ispreferably 50,000-5,000,000 but more preferably 50,000-1,000,000. Whenthe number average molecular weight is less than 50,000, sufficientviscosity is not obtained unless a large amount of the polymer compoundis used, which is uneconomical.

And as pyrolyzing properties are poor (the pyrolysis startingtemperature is the same as for polymer compounds having a molecularweight of 50,000-5,000,000, but time is needed for completedecomposition), pyrolysis residues easily form after brazing.

On the other hand when the number average molecular weight exceeds5,000,000, thread-forming properties are too strong and viscoelasticityis poorer.

Thermal decomposition properties are better for unlike alkylene oxideblocks or random copolymers than for homopolymers of similar alkyleneoxides, which is advantageous for preventing blackening due to pyrolysisresidues after brazing. Also, ethylene oxide-propylene oxide (EO-PO)random copolymers are to be preferred as they have better thermaldecomposition properties than ethylene oxide (EO) homopolymers.

The flux composition of this invention preferably contains 0.5-25 weightparts, and more preferably 1-10 weight parts of polymer compound. Whenthe amount of polymer compound is less than 0.5 weight parts, assufficient viscosity cannot be obtained, the adhesion amount of fluxdrops, and brazing defects arise. On the other hand when the amount ofpolymer exceeds 25 weight parts, the viscosity becomes excessive, theadhesion amount of resin increases, and pyrolysis residues are producedwhen brazing is performed. Moreover, an excessive amount of flux adhereswhich is uneconomical.

The amount of polymer compound may be determined by indication of theviscosity of the flux composition. A suitable viscosity of the fluxcomposition is 150-500 cps at 23° C. The amount of polymer compound maybe set according to its number average molecular weight so that theviscosity lies within this range.

Dispersant

In this invention, water is used as dispersant. Water is odorless. As anorganic solvent is not used, there is no risk of ignition or explosiondue to solvent volatility, procedures are safe to carry out, and sincetoxic solvents are not spilt during operations, hygiene in the workplaceis improved.

Fluoride type flux

According to this invention, it is desirable that a fluoride-type fluxis used. The fluoride type flux may be an aluminum potassium fluorideflux such as AlF₃ -KF, KAlF₄ -K₃ AlF₆, K₃ AlF₆, KAlF₄ and KF-AlF₃ -Al₂O₃, or CsxAlyFz.

The flux composition of this invention contains 5-30 weight parts butmore preferably 5-20 weight parts of fluoride type flux. When the amountis less than 5 weight parts, the flux coating amount is small which maylead to brazing defects. On the other hand when the amount exceeds 30weight parts, the flux allows the brazing material to spread and flowwell, but the appearance of the product is impaired by large amounts ofwhite residue or black spots on the surface of the fillet. For afluoride type flux, a suitable lower limit is 5 weight parts.

Surfactant

It is desirable to add a surfactant to the flux composition of thisinvention in order to increase the dispersing properties of the flux.This surfactant may be a non-ionic type surface active agent such aspolyoxyethylene glycol, polyoxypropylene glycol, polyoxyethylenepolyoxypropyleneglycol, polyoxyethylene alkylphenyl ether,polyoxyethylenealkyl ether, glycerin fatty acid ester, sorbitan fattyacid ester, pentaerythritol fatty acid ester, polyoxyglycerin fatty acidester, polyoxyethylenesorbitan fatty acid ester, polyoxypentaerythrytolfatty acid ester, polyoxyethylene alkylaminoether, or thepolyoxyethylene polyoxypropylene glycol of ethylene diamine, due to theaffinity of these compounds with the fluoride type flux.

The flux composition of this invention preferably contains 0.03-5 weightparts but more preferably 0.04-1 weight parts of the non-ionicsurfactant. When the amount of non-ionic surfactant is less than 0.03,the dispersibility of the flux drops, and the flux easily separates. Onthe other hand when the amount exceeds 5 weight parts, thedispersibility of the flux improves, but pyrolysis residues are producedfrom the non-ionic surfactant during brazing.

Ratio of flux/polymer compound

As stated hereabove, the amount of polymer compound is 0.5-25 weightparts relative to 5-30 weight parts of fluoride type flux. In otherwords, the weight ratio of flux/polymer compound is 0.2-60, a morepreferable weight ratio being 0.5-20. When the weight ratio is less than0.2, sufficient adhesion properties are obtained, but the amount ofpolymer compound for maintaining the flux is too high and pyrolysisresidues are produced during brazing. On the other hand when theaforesaid weight ratio exceeds 60, the amount of polymer compoundrequired to maintain the flux decreases, and adhesion propertiesdecline.

Ratio of flux/non-ionic surfactant

The weight ratio of flux/non-ionic surfactant is 1-1000, but morepreferably 5-500. When this weight ratio is less than 1, thedispersibility of the flux improves, but pyrolysis residues are producedfrom the non-ionic surfactant during brazing. Specifically, this is dueto the fact that the polymer compound decomposes at a temperature of140-200° C., whereas the surfactant decomposes at 200-250° C. On theother hand when the aforesaid weight ratio exceeds 1000, thedispersibility of the flux falls, and the flux easily separates.

Viscosity of flux composition

It is desirable that the viscosity of the flux composition of thisinvention is 150 cps to 500 cps at room temperature (23 degrees). Whenit is less than 150 cps, the adhesion amount of flux drops, and brazingdefects are produced. When the viscosity exceeds 500 cps, more fluxadheres than necessary, so a white residue of flux is produced whenbrazing is carried out.

Brazing Method

According to this invention, brazing of aluminum materials is performedusing the aforesaid flux composition by the following steps.

First, the aforesaid flux composition is applied to the parts of thealuminum materials to be joined. The flux may be coated onto the partsby spraying or immersion, there being no particular limitation on themethod of application. The coating amount is preferably of the order of1-3 g/m² in terms of fluoride type flux amount. For example, a suitableamount (approximately 2 g/m² expressed as aluminum potassium fluorideflux) is coated onto parts of aluminum cladded plates (e.g. an aluminumalloy of JIS3003 core material clad on both sides by JIS4343 materialwith a cladding ratio of 10%) which are to be joined.

Next, the coating surface is heated to vaporize only the water in theflux composition. The fluidity of the composition is then lost, and theflux adheres to the joins due to the adhesive force of the polymercompound. In this heating step, it is necessary to remove the waterwithout removing the polymer compound. Hence the temperature must beless than 150° C. to avoid decomposing the polymer compound, and100-130° C. is particularly to be preferred. The heating time ispreferably of the order of 1-10 minutes.

Next, work is performed which involves subjecting the aluminum materialto friction or vibration. The work is, for example, transporting thematerial from the flux coating shop to the assembly shop, assembling,and transporting from the assembly shop to the polymer pyrolyzing step.As the flux adheres strongly to the joins due to the action of thepolymer compound, there is no risk that it will come off even if thematerials are subjected to friction or vibration.

Next, the flux composition coating surfaces are heated to pyrolyze thepolymer compound, which is thereby removed from the joins so that onlythe flux remains in the joins. The assembly is then sent to the brazingstep. If any polymer compound remains in the joins, pyrolysis residueswill contaminate the fillet due to the high temperature of thesubsequent brazing step, and there is a risk that the strength of thejoints may decrease. In this polymer heating step, therefore, it isdesirable that the polymer compound is pyrolysed while the brazingmaterials are not melted, and it is thus preferable to continue heatingat 150° C. or higher for at least 5 minutes. In particular, 150-200degrees or less is desirable. When heating is continued at thistemperature for five minutes or more, at least 90% of the polymercompound is decomposed, and only flux remains adhering to the joins. Inthis state the adhesive force due to the polymer compound has alreadybeen lost, so care is taken not to subject the coated surfaces tofriction or vibration at this stage.

The clad plates to which the flux composition is adhering are thenassembled into the desired structure, and brazing is performed byheating the assembled structure in a nitrogen atmosphere at 600° C. forseveral minutes. Due to the action of the flux, good brazing quality isachieved.

PREFERRED FORMS OF THE INVENTION

Next, some specific examples and comparative examples will be given tobetter describe the invention.

EXAMPLES 1-5 AND COMPARATIVE EXAMPLES 1-4

(1) Preparation of flux compositions

Flux compositions were prepared for use in the examples and comparativeexamples according to the specifications shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                        Example     Comparative Example                                               1 2 3  4  5 1 2 3  4                                      __________________________________________________________________________    Vehicle                                                                             Polyalkylene oxide polymer #1                                                                2                                                                              --                                                                              3  -- --                                                                               4                                                                              30                                                                              -- --                                     composition                                                                         Polyalkylene oxide polymer #2                                                               --                                                                              10                                                                              -- 0.5                                                                              20                                                                              --                                                                              --                                                                              0.1                                                                              --                                     (wt %)                                                                              Polyalkylene oxide polymer #3                                                               --                                                                              --                                                                              -- -- --                                                                              --                                                                              --                                                                              --  5                                           Non-ionic surfactant #4                                                                      1                                                                               3                                                                              2  2   1                                                                               1                                                                               1                                                                              3   2                                           Water         77                                                                              67                                                                              90 67.5                                                                             69                                                                              --                                                                              44                                                                              86.9                                                                             73                                           Dipropylene glycol                                                                          --                                                                              --                                                                              -- -- --                                                                              75                                                                              --                                                                              -- --                                     Fluoride type flux #5                                                                             20                                                                              20                                                                              5  30 10                                                                              20                                                                              25                                                                              10 20                                     __________________________________________________________________________     Notes)                                                                        #1: Polyethylene oxide polymer; Mol. Wt. 600,000                              #2: EOPO block copolymer (EO: 85%, PO: 15%); Mol. Wt. 100,000                 #3: EOPO random copolymer (EO: 50%; PO: 50%); Mol. Wt. 3,000                  #4: Polyoxyethylene alkylphenol ether                                         #5: "knockLock" (Alkan K.K.)                                             

(2) Evaluation tests

A suitable amount of flux (approximately 2 g/m² expressed as aluminumpotassium fluoride flux) was coated onto join parts of an aluminum alloyof JIS3003 core material clad on both sides by JIS4343 material with acladding ratio of 10%, and moisture was removed.

Next, the clad plates to which the flux composition was adhering wereassembled into the desired structure, the polymer compound in the fluxcomposition was pyrolysed, and brazing was performed by heating theassembled structure in a nitrogen atmosphere at 600° C. for severalminutes.

(3) Evaluation method

(a) Adhesion of flux

O Even if rubbed by hand, flux does not fall off

Δ If touched by hand, flux does not fall off, but it falls off if rubbed

X When touched by hand, the flux falls off

(b) Brazing properties (fillet formation rate)

O Fillet formation rate 100%

Δ Fillet formation rate from 60% to 100%

X Fillet formation rate less than 60%

(c) Combustibility of vehicle (pyrolysis residue after brazing)

O Pyrolysis residue is not produced

X Pyrolysis residue is produced

(d) Ease of coating

O A predetermined amount can be coated to a predetermined brazing part

Δ Coating drips and spreads from predetermined brazing part

X Coating cannot be applied as desired

(e) Odor during application

O Odor is no particular problem

X Unpleasant odor

(f) Dispersibility of flux (separation of flux after leaving all day atroom temperature)

O Flux does not separate

X Flux separates

The examples and comparative examples were evaluated by the abovemethods. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                    Example   Comparative Example                                                 1 2 3 4 5 1 2  3  4                                           __________________________________________________________________________    Evalution                                                                          Flux adhesion properties                                                                 ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                    Δ                                                                          X                                           Method                                                                             Brazing properties                                                                       ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   X ◯                                                                    X  Δ                                          Vehicle combustibility                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   Δ                                                                         ◯                                                                   X  ◯                                                                    X                                                Ease of coating                                                                          ◯                                                                   ◯                                                                   ◯                                                                   Δ                                                                         ◯                                                                   ◯                                                                   X  X  X                                                Odor during operations                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   X ◯                                                                    ◯                                                                    ◯                                    Flux dispersibility                                                                      ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   ◯                                                                   X  ◯                                                                    ◯                               __________________________________________________________________________

From these results, it was found that according to the flux compositionsof these examples, adhesion of flux improved on the parts to be brazed,and brazing could be performed without leaving pyrolysis residues.

EXAMPLES 6-8 AND COMPARATIVE EXAMPLES 5-8

Next, specific examples of the method of brazing aluminum materialsaccording to this invention will be described.

Flux compositions were prepared by blending materials in the proportionsshown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                        Composition                                                                   A    B     C     D     E     F      G                                         (this                                                                              (this (this (this (this (Comparative                                                                         (Comparative                              invention)                                                                         invention)                                                                          invention)                                                                          invention)                                                                          invention)                                                                          example)                                                                             example)              __________________________________________________________________________    Vehicle                                                                             Polyalkylene oxide polymer #1                                                               10    5    20     3     3     5     --                    composition                                                                         Non-ionic surfactant #2                                                                      2    3     3     4     5     3      3                    (wt %)                                                                              Water         78   77    62    73    67    --     82                          Dipropylene glycol                                                                          --   --    --    --    --    77     --                    Fluoride type flux #3                                                                             10   15    15    20    25    15     15                    Flux adhesion properties                                                                          OK   OK    OK    OK    OK    OK     Failed                Unpleasant odor on heating                                                                        NO   NO    NO    NO    NO    YES    NO                    __________________________________________________________________________     Notes)                                                                        #1: Polyethylene oxide polymer; Mol. Wt. 600,000                              #2: Polyoxyethylene alkylphenol ether                                         #3: "knockLock" (Alkan K.K.)                                             

The adhesion of these flux compositions to aluminum materials, and thepresence or absence of an unpleasant odor during heating, were examined.

In the adhesion examination, the flux compositions were sprayed onto aflat test piece of JIS3003 material in a proportion of 2.5 g/m², thesurface was dried at 120° C. for 5 minutes, and the coated surface waswiped with a cloth.

The flux composition was considered to be satisfactory if no more than10% peeled off. The test results are also shown in Table 3.

Brazing tests were also performed using these flux compositions.

The brazing tests were performed during production of the heat exchangerA shown in FIG. 1 and FIG. 2.

In the full view of the heat exchanger A shown in FIG. 1, a plurality oftubular elements 1 are arranged vertically to the left and right,colgate fins 2 being arranged between adjacent tubular fins 1 and at theouter ends of the tubular elements so that the whole forms a one-piececonstruction when brazing is performed.

The tubular elements 1 have expanded tank parts 3a, 3b at both ends inthe length direction, and plates 5 forming flat coolant passages 4 inthe length direction connecting the two tank parts 3a, 3b. Adjacenttubular elements 1 are joined with the tank parts 3a, 3b in contact,adjacent tank parts then being interconnected via coolant holes 6, 6provided in the tank parts 3a, 3b. The aforesaid colgate fins 2 areformed of JIS3203 material sheets having a thickness of 0.12 mm in apredetermined shape.

The tubular elements 1 are formed by superposing two dish-shaped coreplates 7 on their peripheral contact surfaces, and brazing them in aone-piece construction. This core plate 7 is a brazing sheet formed in apredetermined shape from a JIS3003 material core sheet of thickness 0.4mm clad on both sides with a JIS4343 material cover with a claddingratio of 12%.

As shown in FIG. 2, excepting for an outer core plate 7' forming theoutermost tubular element 1, caps 10 which extend outwards are formed atboth ends of the core plates 7, the end walls of these caps 10 beingpierced by three of the coolant holes 6, 6. Both ends of the outer coreplate 7' of the outermost tubular element 1 are flat, the lower endbeing pierced by three of the coolant holes 6.

The tank parts 3a, 3b are formed by superposing the cap parts 10 of twoopposite core plates 7, 7 or 7, 7'. The tank parts 3a, 3a or 3b, 3b ofadjacent tubular elements 1 are then connected via the coolant holes 6.

Ribs 11 are formed running from one cap 10 to the other cap 10 on theinner surfaces of the core plates 7 and at a predetermined interval inthe width direction of the core plates 7. By superposing two of thesecore plates 7, 7 comprising these ribs 11, peripheral join surfaces 7aare brought in contact, and the ribs 11, 11 on the two plates 7, 7 forman alternating arrangement. The tip of each rib 11 comes in contact witha flat part 12 between the ribs 11 on the opposite core plate 7. Pluralcoolant passages are thereby formed extending straight from the lowertank part 3b to the upper tank part 3a inside the coolant passages 4 ofthe tubular elements 1.

Plural tubular elements 1 are therefore brought in contact with the tankparts 3a, 3b of adjacent elements in contact, and enclosing the coreplates 2 between them as shown in FIG. 1.

Herein, the inner layers of the core plates 7 are joined togetherwhereas the tubular element 1 is joined to the colgate fin 2 via theouter layer of the core plate 7. Adjacent tubular elements 1 are joinedtogether via their outer layers of the core plates 7.

In FIG. 1 and FIG. 2, a coolant inlet tube 14 and coolant outlet tube 15are connected to each other via the aforesaid coolant holes 6 in thelower tank parts 3b on the outermost tubular elements 1. Side plates 16are arranged outside the outermost colgate fin 2. These side plates 16are also formed of the same brazing sheet, and are brazed to theoutermost colgate fins 2.

Hence, in this brazing test piece, on the facing contact parts of a pairof core plates, two pieces of JIS3003 material are joined together withJIS4343 brazing material, and at the contact parts of the outer surfaceof a tubular element and a colgate fin, JIS3003 and A3203 material arejoined together by JIS4343 brazing material.

These parts were brazed using one of the flux compositions in Table 3and a combination of the following two steps.

The types of flux composition and combinations of steps, describedhereafter, are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                 Example    Comparative Example                                                6    7      8      5    6    7    8                                  ______________________________________                                        Flux composition                                                                         A      B      D    F    G    A    B                                Step       I      I      I    I    I    II   II                               Brazing properties                                                                       Good   Good   Good NG   NG   NG   NG                               Amount of residue                                                                        Trace  Trace  Trace                                                                              Trace                                                                              Trace                                                                              Large                                                                              Large                            ______________________________________                                         Note) Underlines in the table signify outside the range of this invention

Step I (Method of this Invention)

i) A predetermined amount of flux composition was spray coated on thecore plates 7, 7' and side plate 16.

(ii) The core plates 7,7' and side plates 16 were heated at 100 degreesfor 5 minutes to remove the water in the flux composition.

(iii) The core plates 7,7' and side plate 16s were transported, and theheat exchanger was assembled with the colgate fins 2, coolant inlet pipe14 and coolant outlet pipe 15.

(iv) The assembled heat exchanger was heated to 150° C. for 5 minutes tothermally decompose the polymer compound in the flux composition.

(v) The brazing was melted by heating at 600° C. for 5 minutes, and thecomponent parts thereby joined.

Step II (Method of Comparative Examples)

(i) A predetermined amount of flux composition was spray coated on thecore plates 7,7' and side plates 16.

(ii) The core plates 7, 7' and side plates 16 were heated to 150° C. for5 minutes to remove water and thermally decompose the polymer compoundin the flux composition.

(iii) The core plates 7,7' and side plates 16 were transported, and theheat exchanger was assembled with the colgate fins 2, coolant inlet pipe14 and coolant outlet pipe 15.

(iv) The brazing was melted by heating at 600° C. for 5 minutes, and thecomponent parts were thereby joined.

After brazing, the brazing properties were evaluated from the appearanceof the fillet, and from visual observation of the amount of flux residuethat had peeled off inside the heat exchanger. The test results areshown in Table 4.

From the results of Table 3 and Table 4, it was found that the accordingto this method of this invention, the flux composition has good adhesionproperties. After coating, only water is removed leaving the flux toadhere strongly so that transport, fitting and other operations whichmight otherwise cause peeling of flux can be performed. As the resinbinder is then thermally decomposed, exactly the right amount of flux issupplied when the brazing is melted on joins. Further, by adopting thesesteps, peeled flux residues inside brazing parts were avoided.

Industrial Field of Application

As described hereabove, the brazing method for aluminum materialsaccording to this invention uses a flux composition comprising 5-30weight parts of a fluoride type flux, 0.5-25 weight parts of a polymercompound having alkylene oxide repeating units of number averagemolecular weight 50,000-5,000,000 and water as the remainder, so theflux adheres strongly to aluminum materials due to its viscosity.

As the dispersant is water, the flux does not emit an unpleasant odoreven when heated, work can be performed in a good environment, andoperations with the flux are safe for humans.

After the flux composition is coated onto the aluminum materials to bejoined, the coating surfaces are heated to remove water, the coatedsurfaces are again heated to pyrolyze the polymer compound, and brazingis then performed. Even if the aluminum materials are subjected tooperations involving friction or vibration after heating to remove waterbut prior to heating to pyrolyze the polymer compound, flux does notfall off during the operations and the amount of flux left on joins whenthe brazing is melted is exactly the right amount, so a good brazingquality is achieved.

Flux residues do not remain inside and outside brazing products, hencecoating defects, decrease of corrosion resistance and emission ofunpleasant odor which such residues would cause are suppressed. Inparticular, regarding the brazing of heat exchangers, the problem ofincreased flowpath resistance due to flux residues is eliminated.

In the aforesaid brazing method, heating to remove water is performed ata lower temperature than 150° C., so only water is removed, the polymercompound remains, and the high adhesive force of the latter can beefficiently exploited.

By then heating at a temperature of 150 or higher or preferably 150-200°C. for 5 minutes or more to remove the polymer compound, the polymercompound is completely thermally decomposed.

As the brazing is melted after having removed the polymer from joins, agood brazing quality is achieved.

What is claimed is:
 1. A flux composition for the brazing of aluminummaterials characterized in comprising 0.5-25 weight parts of a polymercompound having alkylene oxide repeating units of number averagemolecular weight 50,000-5,000,000, 5-30 weight parts of a fluoride typeflux and water added to make the composition up to 100 weight parts. 2.A flux composition for the brazing of aluminum materials as defined inclaim 1 further comprising 0.03-5 weight parts of a non-ionicsurfactant.
 3. A flux composition for the brazing of aluminum materialsas defined in claim 2 wherein a weight ratio of flux/non-ionicsurfactant is 1-1000.
 4. A flux composition for the brazing of aluminummaterials as defined in claim 2 wherein a weight ratio of flux/non-ionicsurfactant is 5-500.
 5. A flux composition for the brazing of aluminummaterials as defined in claim 1 wherein said polymer compound hasrepeating units of ethylene oxide and/or propylene oxide.
 6. A fluxcomposition for the brazing of aluminum materials as defined in claim 1wherein said polymer compound is a polymer compound having a numberaverage molecular weight of 500,000-1,000,000.
 7. A flux composition forthe brazing of aluminum materials as defined in claim 1 wherein anaddition amount of said polymer compound lies in the range of 1-10weight parts.
 8. A flux composition for the brazing of aluminummaterials as defined in claim 1 wherein an addition amount of a fluoridetype flux lies in the range of 5-20 weight parts.
 9. A flux compositionfor the brazing of aluminum materials as defined in claim 1 wherein saidfluoride type flux is an aluminum potassium fluoride flux.
 10. A fluxcomposition for the brazing of aluminum materials as defined in any ofclaim 1, wherein said fluoride type flux is at least one of AlF₃ -KF,KAlF₄ -K₃ AlF₆, K₃ AlF₆, KAlF₄, KF-AlF₃ -Al₂ O₃ or Cs_(x) Al_(y) F_(z).11. A flux composition for the brazing of aluminum materials as definedin claim 1 wherein the weight ratio of flux/said polymer compound liesin the range 0.2-60.
 12. A flux composition for the brazing of aluminummaterials as defined in claim 1 wherein the weight ratio of flux/saidpolymer compound lies in the range 1-20.
 13. A method for the brazing ofaluminum materials wherein a flux composition comprising 0.5-25 weightparts of a polymer compound having alkylene oxide repeating units ofnumber average molecular weight 50,000-5,000,000, 5-30 weight parts of afluoride type flux and water added to make the composition up to 100weight parts, is coated onto aluminum parts to be joined, the coatedsurfaces are heated to remove water, the coated surfaces are heated topyrolyse the polymer compound, and heat is applied to perform brazing.14. A method for the brazing of aluminum materials as defined in claim13 wherein heating to remove water is performed at a temperature lessthan 150° C.
 15. A method for the brazing of aluminum materials asdefined in claim 13 wherein heating to remove water is performed at atemperature in the range 100-130° C. for 1-10 minutes.
 16. A method forthe brazing of aluminum materials as defined in claim 13 wherein heatingto pyrolyse said polymer compound is performed at a temperature in therange 150° C. or higher for 5 minutes or more.
 17. A method for thebrazing of aluminum materials as defined in claim 13 wherein heating topyrolyse said polymer compound is performed at a temperature in therange 150-200° C. for 5 minutes or more.
 18. A method for the brazing ofaluminum materials as defined in claim 13 wherein the coating amount ofsaid flux composition is in the range 1-3 g/m² expressed as fluoridetype flux.
 19. A method for the brazing of aluminum materials as definedin claim 13 wherein an addition amount of said polymer compound lies inthe range of 1-10 weight parts.
 20. A method for the brazing of aluminummaterials as defined in claim 13 wherein an addition amount of afluoride type flux lies in the range of 5-20 weight parts.